A piece of furniture that oscillates about an axis, for instance a baby cradle, Hollywood swing, child's swing, or infant's bed, is typically operated manually either by the user or a person tending the user, but may have some kind of electric or windup drive to prevent the oscillation from degrading, that is the rocking furniture from stopping. The swinging action is often desirable to soothe an infant or to amuse an older user of the rocking furniture.
The typical drive system as described in U.S. Pat. No. 4,028,753 of Rios, German 3,042,314 of Gullilen, or German 3,530,527 of Schmidt has a rotary motor that sits on the ground or on a stationary frame and that drives an eccentric crank arm that is in turn attached to the rocking part of the piece of furniture. Such a system is often very energy inefficient since it imposes a movement on the piece of furniture that is determined by the motor speed and that has no relation to the natural rocking frequency of the item. German utility model 7,520,683 of Buchfelder proposes a potentially adjustable electromagnetic drive intended to follow the furniture's eigenfrequency, that is its natural oscillation frequency, but such systems are normally fairly complex and consume considerable energy.